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I've been reading this Wikipedia - Electrical Load topic and there is a section which is confusing me... So what you do is go to the "A more technical approach" section in this topic and then read the 4th line which starts with "With no load (open-circuited terminals)...".

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Now the line says that "With no load (open-circuited terminals), all of Vs falls across the output; the output voltage is Vs." But how? Isn't there be a voltage drop across the resistor Rs? If not, why not?

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No, the page is corrrect. The voltage drop across the resistor is equal to the current through the resistor multiplied by the resistance.

V=IR

The current is zero, therefore the voltage drop is zero, and Vs is present at the output.

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Isn't there be a voltage drop across the resistor Rs?? If not, why not??

No, there is zero volts across a resistor, by Ohm's Law, when there is zero current through the resistor.

If the load is an open circuit, there is zero current through \$R_S\$ and so, the voltage across \$R_S\$ is \$0V\$.

By KVL:

$$V_S = V_{Rs} + V_{OUT} = 0V + V_{OUT}$$

and so,

$$V_S = V_{OUT}$$

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